A conventional integrated optoelectronic circuit comprises an optical device, such as a light emitting diode, photodiode etc., mounted on a ceramic substrate, an electronic device also mounted on the ceramic substrate, lead patterns disposed on the ceramic substrate for connecting the optical and electronic devices, an optical fiber, one end of which faces the optical device, and external terminals through which power is supplied to the electronic device and through which the electronic device is connected to ground.
In operation, modulated optical signals are supplied through the optical fiber to, for instance, the photodiode which is supplied with bias current through the lead patterns from the electronic device an output of the photodiode is supplied through the lead patterns to the electronic device. In this situation, optimum light axis coupling between the optical fiber and photodiode is obtained when the maximum output is produced by the electronic device.
On the other hand, optimum light axis coupling between the optical fiber and light emitting diode is obtained when the maximum output is supplied from the optical fiber.
Another conventional integrated optoelectronic circuit comprises an optical device, such as a light emitting diode, photodiode etc., mounted on a ceramic substrate, an electronic device also mounted on the ceramic substrate, led patterns disposed on the ceramic substrate for connecting the optical and electronic devices, an optical fiber, one end of which faces facing the optical device, and external terminals respectively connected to the lead pattern through which a bias voltage is applied to the electronic and optical devices and through which the electronic and optical devices are connected to ground.
In operation, the bias voltage is applied through one of the external terminals to the optical device, while the electronic device is not supplied with power. In a case where the optical device is a light emitting diode, the light emitting diode is operated continuously to emit light which is supplied to the optical fiber. Under such a condition, optimum light axis coupling between the optical fiber and light emitting diode is obtained when an output of the optical fiber is at its maximum. In a case where the optical device is a photodiode, on the other hand, the photodiode is supplied continuously with light from the optical fiber. Under such a condition, optimum light axis coupling between the optical fiber and photodiode is detected by checking output current flowing through the other external terminal from the photodiode.
According to the former conventional integrated optoelectronic circuit, however, there is a disadvantage in that apparatus for modulating input light to be supplied to the optical fiber and for measuring high frequency signals supplied from the electronic device must be prepared.
According to the latter conventional integrated optoelectronic circuit, further, there are disadvantages. The properties of the optical and electronic devices are adversely affected because noise is carried on the external terminals. The ratio between signal and noise (S/N ratio) is also reduced for the same reason. The optimum light axis coupling between the optical fiber and a light receiving device such as a photodiode is difficult to determine because the electronic device produces digital signals which are based on current signals amplified therein.